Getting data from the Impedance Analyzer 4294a

[zingkov]

First of all, I must admit that this is my very first time using Labview. What I have done so far is merely following some basic examples provided in the wonderful NI demos/webcasts.
 
What I want to do now is simple:
1. Reproduce the graph displayed on the screen of Agilent Impedance Analyzer 4294 in Labview Front Panel.
2. Save all the data into my computer hard disk in either txt or EXCEL format.
 
I am using Labview 8.5 (with GPIB connection). I have downloaded the NI 488.2, NI VISA and NI instrument driver for 4294a. The connection worked just fine. I have browsed through all the provided examples in the driver. However, most of the examples only display the measurement value of a specific parameter. None of them show the entire graph or allow us to specify the folder which I want to store the entire data to. I suppose with simple modifications at the Labview block diagram, this can be easily done. But I just have no idea how to do even that.
 
I earnestly hope some experts here can give me some clues. Thank you very very much!

[Sendtohen]

I have downloaded the drivers.  I was able to get the data, there seems to be some performance issues.  I was able to capture the data, but when I try to read it out it is given me a VISA:  (Hex 0x3FFF0006) issue and the error code of 1073676294.  I know this is a number of byte problem, but I was not able to resolve it. It is take really long while my requirement is on the order of milisecs.  Please advice. Henry

[smercurio_fc]

Was that an actual error? Was the "status" boolean in the error cluster actually on? If not, then that's a warning (using NI's error/warning convention). My guess is that you're using a serial connection, and that you have termination character enabled, meaning the read is stopping once it sees the termination character (probably a linefeed). As for your speed issue: I woulnd't count on getting data that fast, especially if you're using serial. Even GPIB is questionable since you have so many software layers to get through. If you have high-speed requirements you may need to look at alternative ways of getting the data, such as using a DAQ board.

[Sendtohen]

I am sorry, maybe I am not being clear enough.  I am collecting data through GPIB.  I am using the downloaded drivers.  Whenever I try to collect a set of data, it would take over 10 secs.  As i track the timing of each sub vi.  I tracked it down to the "Read Data unknown length" inside the "Read Data and memory array.vi" which takes up most of the time.  Is 10 seconds normal?  I would just like to collect some data at the speed of 1 sec.  Any help would be appreciated.Henry

[smercurio_fc]

That sounds like a timeout issue. That subVI just loops around until the VISA Read returns with no bytes. Seems a bit clumsy to me, as you can get into a situation where a single read could return no bytes, yet there's still data there. One thing that you can try is to replace the call to the "Read Data Unknown Length" with a VISA Read in which you wire a really big number for the number of bytes to read. The VISA Read will read as many bytes as available - basically until is sees EOI. Sort of like this:<img src="Failed to load image: http://forums.ni.com/attachments/ni/170/331782/1/read%20mod.PNG"> You will need to determine what a sufficiently large number is based on the number of points and the data size (i.e., number of bytes per point). This should be in the instrument documentation.Message Edited by smercurio_fc on 06-14-2008 11:36 AM


read mod.PNG:
http://forums.ni.com/attachments/ni/170/331782/1/read mod.PNG